By July, most songbirds are in the final stages of raising their young, but not the American Goldfinches. They are just getting started.
Notoriously late nesters, goldfinches have been waiting for the thistles to bloom. When this happens in July, it signals the goldfinches that they can start building their nests made primarily of the silver fibers and down of thistle blooms. Generally, the nest is built in the fork of a horizontal tree limb, 4 to 14 feet above the ground. Here the female builds a durable, neat cup of thistle and cattail fibers, so dense that it will hold water. In it she lays 4 to 6 pale blue to white eggs and then she incubates them for 12 to 14 days, until they hatch. The attentive male often feeds his mate while she sits on the nest.
By the time the eggs hatch, the thistle has gone to seed, which is perfect timing for feeding young goldfinches. The parents nourish this chicks by consuming the thistle seed themselves, and then regurgitating the partially digested, milklike cereal into the mouths of their nestlings. This is as close as birds come to mammals that feed their young milk from mammary glands.
Baby goldfinches are fully feathered and out of the nest 10 to 16 days later. Almost immediately, they join their parents at bird feeders across America. That’s when many people suddenly notice “so many goldfinches this year.”
George H. Harrison